1. Technical Field
The present invention relates to optical instruments and more particularly, to optical instruments with temperature compensation mechanism for focal length variations.
2. Discussion of the Related Art
Optical instruments tend to suffer from focal length variation due to changes in the temperature of the ambient. This is usually because the optical indices of the lenses tend to change over temperature. Additionally, the geometry of the lenses may further change due to temperature variation and so does the focal length of the set of lenses.
Several solutions for the temperature-related focal length variation problem are known in the art. FIG. 1 shows one such solution, in which optical instrument 10 includes, for example, one set of lenses 20A-20F within optical instrument 10 that has an image sensor 60 affixed thereto. Lenses 20A-20F are all affixed to identical members of temperature compensation 50A and 50B. Temperature compensation members 50A and 50B may be comprised each of two or more portions of different materials selected due to their respective temperature expansion coefficient. Specifically, the length of each one of the portions and the materials are selected so that the any change in the focal length of optical instrument 10 due to changes in the geometry of lenses 20A-20F due to temperature change is compensated by the expansion of temperature compensation members 50A and 50B. In this manner, within a range of temperatures, the effective focal length of optical instrument 10 remains the same.